1. Field of the Invention
The present invention relates to a starch composition containing a relatively high proportion of so-called "resistant starch" structures.
2. Background Information
It has been known for many years that starches, which commonly consist of varying proportions of amylose and amylopectin, may be subjected to an enzymatic treatment which reduces the content of the highly branched amylopectin and increases the content of short-chain amylose structures (see, for example, U.S. Pat. No. 3,729,380). It is also known that the products of such enzymatic treatment are more prone to retrogradation than normal starches and produce in this manner compositions containing increased amounts of resistant starch structures. Resistant starch (RS) is resistant to attack by alpha-amylase and may be used therefore as a low calorie bulking component in food compositions so contributing to the dietary fibre content of such compositions.
The treatment of the starch with the debranching enzyme takes place in an aqueous slurry which, for handling reasons, cannot be too concentrated. It would clearly be attractive therefore to be able to use a starchy composition at a higher concentration than normal while at the same time increasing the amount of RS formed as a proportion of the starchy material treated. EP 564 893 A describes and claims a process for the production of a RS product containing at least about 15% RS in which an aqueous slurry of starch containing at least 40% amylose is gelatinised and debranched by treatment with a debranching enzyme which hydrolyses 1,6-glucosidic bonds in the starch molecules, the debranched product subsequently being retrograded to produce RS. The optimum starch concentration in the aqueous slurry is said to be about 15% and the Examples of 564 893 A illustrate the process by using starch slurries containing 14% to 17% starch respectively. The starch starting material contains at least 40% amylose and for a corn (maize) starch containing 25% amylose it is shown that no RS is formed in the process. As the percentage of amylose in the starch starting material increases above 40% so does the RS in the product of the process until a starch containing 100% amylose is shown to produce a product containing 50.3% RS.